1. Field of the Invention
The present invention relates to an image readout apparatus such as a facsimile machine, image scanner, or the like; and an image readout lens employed as an optical system thereof. In particular, the present invention relates to an image readout lens for reducing or enlarging images, and an image readout apparatus using the same.
2. Description of the Prior Art
Imaging lenses for reading out images employed in facsimile machines, image scanners, and the like of a type in which a reduced or enlarged image of an original is formed onto an imaging device such as CCD are basically required to have a high resolution at the imaging magnification in use, a large amount of marginal illumination, and a low distortion. In addition, along with recent demands for making the whole optical apparatus more compact and less expensive, these lenses are required to have a compact size and to be made at a lower cost.
As an imaging lens which can fulfill these requirements, one having a four-element configuration disclosed in Japanese Unexamined Patent Publication No. 9-101452 has been known.
Though the four-element imaging lens disclosed in the above-mentioned publication can yield a favorable quality of readout images over a wide angle, brighter image readout lenses have been desired for use in line sensors for copiers and the like in view of demands for higher readout speed.